At present, the urban sewage treating plants in our country mainly adopt the conventional secondary activated sludge treatment to treating sewage. With the increase of sewage, the treatment capacity should be reformed to increase too. While if this reform is based on the conventional process i.e. the above secondary activated sludge treatment, it will lead to the high investment cost, high energy consumption, high operation and management requirements and easy secondary pollution, which does not meet the requirements of sustainable development. If the conventional biological aeration tank is adopted, the organic matter in sewage can be removed effectively, but the removal ability of nitrogen and phosphorus was low; if the membrane bioreactor i.e. membrane separation technology is adopted, the quality of output water is very high, but the investment and operating costs are expensive, which greatly restricts the wide application of this technology; if other chemical and physical treatment technology is adopted, there are problems such as high investment and operating costs, unstable quality of output water and secondary pollution.
Artificial wetland technology is a sewage treatment technology since 1970s, because of the advantages such low construction investment and operation management cost, low energy consumption, long operation period and stable operation, it has been gradually applied to the domestic sewage treatment in small and medium-sized cities and rural areas.
The technical information about artificial wetland technology can be found in the published Chinese patent documents, typically as the “a sewage treatment and device thereof” recommended by granted patent CN1163427C, which includes the following steps: firstly, making sewage pass through settling pond to removing hard grain and suspension; then feeding the sewage into flowing bed in which the gravels are filled and the aquatic plant and hydrophytes are planted so as to further reduce suspension in sewage and reduce COD of sewage; then feeding the sewage into downward artificial wetland bed (downward artificial wetland in the patent), and finally into upward artificial wetland bed (upward artificial wetland in the patent). Compared with the conventional secondary activated sludge treatment, this technology can achieve the technical effect recorded in the description, page 2, line 21 to line 27. But there are some disadvantages in this patent: first is the water in flowing bed is fed into downward artificial wetland bed with a horizontal flow rather than a vertical flow, so the processing efficiency is limited; second is denitrification reaction is before nitration reaction, which is bad for denitrification reaction; third is there are a lot of links from the sewage feeding into sedimentation tank to upward artificial wetland bed, and each link is not an organic whole, so the sewage treating procedure is very long. Another solution provided by CN103274529A is “a device and method for prolonging service life of integrated vertical-flow constructed wetland”, in which sewage feed into artificial wetland bed (artificial wetland unit) with vertical flow. Compared with the horizontal flow in the above patent CN1163427C, sewage treatment efficiency improved, and objectively achieved the technical effect concluded in the description, paragraph 13. But because the wetland unit body is divided into two wetland units by the partition wall, and the recycling treatment of sewage is achieved through two independent sets of water distribution system and water collecting system, there are disadvantages such as complex structure, high cost and complicated operation.
Based on the above mentioned technologies, the applicant has made a long lasting and beneficial exploration and repeated experiments, and finally formed the following technical solutions to be introduced.